全文获取类型
收费全文 | 61159篇 |
免费 | 3916篇 |
国内免费 | 7篇 |
专业分类
65082篇 |
出版年
2023年 | 447篇 |
2022年 | 377篇 |
2021年 | 810篇 |
2020年 | 752篇 |
2019年 | 735篇 |
2018年 | 1932篇 |
2017年 | 1805篇 |
2016年 | 2349篇 |
2015年 | 3080篇 |
2014年 | 3027篇 |
2013年 | 4078篇 |
2012年 | 4908篇 |
2011年 | 4380篇 |
2010年 | 2721篇 |
2009年 | 2078篇 |
2008年 | 3394篇 |
2007年 | 3193篇 |
2006年 | 3001篇 |
2005年 | 2560篇 |
2004年 | 2484篇 |
2003年 | 2214篇 |
2002年 | 2042篇 |
2001年 | 1375篇 |
2000年 | 1366篇 |
1999年 | 1043篇 |
1998年 | 433篇 |
1997年 | 313篇 |
1996年 | 322篇 |
1995年 | 305篇 |
1994年 | 236篇 |
1993年 | 220篇 |
1992年 | 522篇 |
1991年 | 443篇 |
1990年 | 398篇 |
1989年 | 395篇 |
1988年 | 391篇 |
1987年 | 349篇 |
1986年 | 331篇 |
1985年 | 334篇 |
1984年 | 337篇 |
1983年 | 230篇 |
1982年 | 213篇 |
1980年 | 170篇 |
1979年 | 207篇 |
1978年 | 202篇 |
1975年 | 194篇 |
1974年 | 211篇 |
1973年 | 219篇 |
1972年 | 181篇 |
1969年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
J M Gandarias L Casis R Múgica G Aréchaga M Ramírez 《Revista Espanola de Fisiología》1989,45(1):89-93
A comparative study of brain aminopeptidase activity between 18 month old male rats and young adults of 3 months has been carried out utilizing the arylamides Leu-, Arg-, Lys-, Tyr- and Asp-beta-naphthylamide as substrates. Statistical analysis of results showed no significant differences either in areas studied or for enzymatic activities detected when both ages were compared. Two different patterns of regional distribution of enzymatic activity were observed: One came to be as a result of the use of Lys-, Arg-, Leu- or Tyr-beta-naphthylamide and the other as a result of the use of Asp-beta-naphthylamide. 相似文献
92.
93.
A method for sequential estimation of nuclear DNA and silver staining of nucleoli in plant cells is described. Feulgen staining is done first and nuclear DNA estimated by absorption cytophotometry. Following this, the slides are stained with AgNO3. The method has been used to study the process of nucleolar fusion in garlic (Allium sativum L.) meristem root tip cells. It was found that during interphase nucleoli rarely fused, thus most fusion must have occurred before the G1 phase of the cell cycle. 相似文献
94.
In renal sac nephrocytes of Helix aspersa, intracellular calcium has been localized using the oxalate-pyroantimonate (OPA) and phosphate-pyroantimonate (PPA) methods. Pyroantimonate precipitates are preferentially localized in the excretory spherule and in vesicles located in the basal and lateral regions of the nephrocyte. Such vesicles appear to release their content into the excretory vacuole. Calcium may interact with diverse types of molecules present in the excretory vacuole, thus favouring stabilization and packaging of the excretory spherule. 相似文献
95.
Summary Germination of condiospores fromA.niger in very concentrated suspension was required to inoculate solid fermentation media, but a germination self-inhibitor was detected in spores. It was found that the inhibitory effect depended on the composition of the medium and was reduced when glucose was used as a carbon source. The effect of the self-inhibitor was eliminated by washing the spores and using glucose and a protein nitrogen source in the germination medium. By this method it was possible to increase about 100 times (106 to 108) spore concentration, keeping more than 90% germination. 相似文献
96.
Alpha 2-adrenoceptor activation inhibits cyclic AMP accumulation in fat cells from many species. However, the presence of alpha 2-adrenoceptors in rat adipocytes has been difficult to demonstrate. We observed that alpha 2-adrenergic activation inhibits forskolin-stimulated cyclic AMP accumulation both in rat and hamster adipocytes; UK 14304, p-amino clonidine and clonidine were the agents with higher efficacy. The effect of UK 14304 was blocked by yohimbine but not by prazosin demonstrating the involvement of alpha 2-adrenoceptors. Pertussis toxin blocked the alpha 2-adrenergic effect. Our results demonstrate the presence in rat fat cells of alpha 2-adrenoceptors coupled to adenylate cyclase via "Gi". 相似文献
97.
98.
High-molecular DNA from chicken erythrocytes interacts with 1,2-dipalmitoylphosphatidylcholine in unilamellar liposomes, both in the presence and absence of Mg2+ ions. This interaction results in a phase separation in liposome membranes. The new phase induced by DNA and Mg2+ has a higher gel-liquid crystal phase transition temperature as measured by microcalorimetry. In the liquid crystalline state, the 16- and 5-doxyl stearic acid spin labels indicate changed local bilayer properties at the label position in the new phase. 相似文献
99.
A study of the monomeric chromophore of the oligopeptides netropsin (1), distamycin III (2), and distamycin V (3) by polarization spectroscopy techniques and molecular orbital calculations is reported. Linear dichroism spectra of the monomeric model compounds 1-methyl-2(ethylcarbamoyl)-4-acetamido-pyrrole (4) and 1-methyl-2(ethylcarbamoyl)-pyrrole (5) dissolved and oriented in lyotropic and thermotropic liquid crystals provide, together with the magnetic CD spectra, experimental checks of the theoretical calculations. The polarization directions of the investigated transition obtained by these means in this study allow us to build up in the following paper the exciton states of (1)-(3) and these provide a stereochemical interpretation of the flow linear dichroism spectra of the complexes of DNA with (2) and (3). 相似文献
100.